PROJECT SUMMARY/ABSTRACT Health disparities in tobacco and other substance use are well documented between sexual minorities (e.g., lesbian, gay, bisexual, or queer) and heterosexual individuals across the lifespan. In particular, sexual minority youth (SMY) initiate tobacco use at younger ages and smoke cigarettes at higher rates than their heterosexual counterparts. Stigma and discrimination-related stressors specific to their minority sexual orientation (i.e., minority stressors) contribute to our understanding of health disparities among SMY. Minority stressors are often experienced daily by SMY. As such, SMY may smoke cigarettes as a way to cope with negative affect elicited by these stigma-based stressors. In fact, cross-sectional research shows that minority stressors are correlated with cigarette smoking and other substance use among SMY. Important limitations of the extant literature, however, include overreliance on cross-sectional and retrospective self-report data, failure to account for within- and between-individual differences in minority stressors and smoking behaviors, and lack of discernment of unique contributions of minority stressors on smoking beyond individual differences in daily general stressors, lifetime cumulative stress, and mental health. In addition, we know very little about the mediating mechanisms between minority stressors and cigarette smoking. Consistent with Institute of Medicine and the NIH Sexual and Gender Minority Research Coordinating Committee's call to expand our understanding of factors contributing to SMY?s higher levels of tobacco and other substance use, and in response to NIH PA-15-263?s focus on sexual minority health research, we propose an innovative exploratory study (R21). We propose a rigorous examination of the effects of minority stressors on cigarette smoking in real time in the natural environment among SMY using electronic experience sampling methods, specifically ecological momentary assessment (EMA). Our primary aims are to examine: a) the relationship between minority stressors and proximal changes in smoking in real time in the natural environment among 60 SMY who are regular smokers using EMA over a 30-day period; b) the effects of minority stressors on proximal changes in affect and craving; and, c) the mediating effects of affect and craving on the relationship between minority stressors and cigarette smoking. Our secondary aims of this study are to examine the effects of minority stressors on proximal changes in other substance use as well as to test resilience resources and contextual risk factors that might be associated with smoking. Findings from this exploratory study would have important theoretical implications for minority stress theory and inform the development of culturally sensitive smoking prevention and cessation interventions for SMY, targeting specific within-individual mechanisms as well as contextual factors. The proposed R21 will also provide pilot data for large scale research to more rigorously test the fine-grained psychosocial resilience and risk mechanisms associated with SMY?s smoking.